added middleware to wrap ochttp server handler

Signed-off-by: Frederic BIDON <fredbi@yahoo.com>

tracer/middleware.go

@@ -0,0 +1,126 @@
+package tracer
+
+import (
+	"net/http"
+
+	"go.opencensus.io/plugin/ochttp"
+	"go.opencensus.io/trace"
+	"go.opencensus.io/trace/propagation"
+)
+
+// Middleware that wraps go.opencensus.io/plugin/ochttp for a more idiomatic usage.
+//
+// Options available to ochtpp.Handler are exposed here as Options.
+func Middleware(opts ...MiddlewareOption) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		traceHandler := &ochttp.Handler{
+			Handler: next,
+		}
+
+		if len(opts) == 0 {
+			return traceHandler
+		}
+
+		o := applyMiddlewareOptions(opts)
+		traceHandler.IsPublicEndpoint = o.isPublicEndpoint
+		traceHandler.IsHealthEndpoint = o.healthEndpointFunc
+		traceHandler.FormatSpanName = o.spanNameFunc
+
+		if len(o.startOptions) > 0 {
+			to := trace.StartOptions{}
+			for _, apply := range o.startOptions {
+				apply(&to)
+			}
+			traceHandler.StartOptions = to
+		}
+		if o.getStartOptions != nil {
+			traceHandler.GetStartOptions = o.getStartOptions
+		}
+		if o.format != nil {
+			traceHandler.Propagation = o.format
+		}
+		if o.withRoute != "" {
+			return ochttp.WithRouteTag(traceHandler, o.withRoute)
+		}
+		return traceHandler
+	}
+}
+
+type (
+	MiddlewareOption func(*middlewareOptions)
+
+	middlewareOptions struct {
+		withRoute          string
+		format             propagation.HTTPFormat
+		getStartOptions    func(*http.Request) trace.StartOptions
+		healthEndpointFunc func(*http.Request) bool
+		spanNameFunc       func(*http.Request) string
+		startOptions       []trace.StartOption
+		isPublicEndpoint   bool
+	}
+)
+
+func applyMiddlewareOptions(opts []MiddlewareOption) middlewareOptions {
+	var o middlewareOptions
+
+	for _, apply := range opts {
+		apply(&o)
+	}
+
+	return o
+}
+
+// WithFormat overrides the trace propagation format (default is B3).
+func WithFormat(format propagation.HTTPFormat) MiddlewareOption {
+	return func(o *middlewareOptions) {
+		o.format = format
+	}
+}
+
+// WithRoute decorates the trace with an extra route tag
+func WithRoute(route string) MiddlewareOption {
+	return func(o *middlewareOptions) {
+		o.withRoute = route
+	}
+}
+
+// IsPublicEndpoint instructs the tracer to consider incoming trace metadata as
+// a linked trace rather than a parent (for publicly accessible servers).
+func IsPublicEndpoint(enabled bool) MiddlewareOption {
+	return func(o *middlewareOptions) {
+		o.isPublicEndpoint = enabled
+	}
+}
+
+// IsHealthEndpoint instructs the tracer to skip tracing when the function returns true.
+// a linked trace rather than a parent (for publicly accessible servers).
+//
+// By default, paths like /healthz or /_ah/health are filtered out from tracing.
+func IsHealthEndpoint(filter func(*http.Request) bool) MiddlewareOption {
+	return func(o *middlewareOptions) {
+		o.healthEndpointFunc = filter
+	}
+}
+
+// WithStartOptions enables trace start options such a overriding the span kind or
+// adding a sampler. See go.opencensus.io/trace.StartOptions.
+func WithStartOptions(opts ...trace.StartOption) MiddlewareOption {
+	return func(o *middlewareOptions) {
+		o.startOptions = opts
+	}
+}
+
+// WithGetStartOptions enables trace start options such a overriding the span kind or
+// adding a sampler, on a per request basis.
+func WithGetStartOptions(fn func(*http.Request) trace.StartOptions) MiddlewareOption {
+	return func(o *middlewareOptions) {
+		o.getStartOptions = fn
+	}
+}
+
+// WithFormatSpanName injects a function to determine the span name according to the request.
+func WithFormatSpanName(fn func(*http.Request) string) MiddlewareOption {
+	return func(o *middlewareOptions) {
+		o.spanNameFunc = fn
+	}
+}